The present invention relates to apparatus for controlling registration, and more particularly to apparatus for controlling the registration of two continuously moving layers of material, and articles made thereby.
Various products are fabricated in a continuous production line by the sequential addition of components to previously supplied components. This is particularly advantageous when one or more of the components can be supplied in the form of a single continuous layer. For example, in the formation of disposable absorbent articles, such as training pants, diapers, incontinence articles, feminine care products, or the like, a layer is normally supplied at a point in the fabrication line in the form of a continuous roll, and absorbent pads, waist elastic bands, leg elastic bands, stretchable side panels, and/or other elements or components can be supplied at different points in the fabrication line as discrete objects.
Various methods and apparatus are available for bringing the components of a single product together so that the components in the composite product are in a desired relation with respect to each other. In bringing these components properly together, various known methods and apparatus are used to note the position of a particular component, and then to adjust the position of subsequent components in order to properly position them.
A problem encountered with these types of methods and apparatus is that they do not adequately compensate for the stretching of a continuously moving layer. During manufacturing processes of this type, a continuously moving layer is subjected to various tensions caused by it being driven or pulled through the process for handling. This tension causes the continuously moving layer to stretch, or to relax, thereby resulting in some components being undesirably positioned or, once positioned, shifted out of position. Since it is virtually impossible to maintain a constant tension on the continuously moving layer, the degree of stretching varies throughout the process. Consequently, even though an earlier positioned component may initially be within an acceptable position range, the stretching of the continuously moving layer may result in the component being outside of the acceptable position range in the final composite product.
Another problem with current methods and apparatus is that they do not provide an adequate means for registering two continuously moving layers, and particularly when one of the layers has a pre-printed or pre-positioned component or the like that is to be registered with a pre-printed or pre-positioned component or the like on the other of the layers during the manufacture of a plurality of products having a desired registration of components.